Method of making a capacitor with oxygenated metal electrodes and high dielectric constant materials

ABSTRACT

A stabilized capacitor using high dielectric constant dielectric materials, such as Ta 2 O 5  and Ba x Sr (1−x) TiO 3 , and methods of making such capacitors are provided. A preferred method includes chemical vapor depositing a lower electrode, oxygen doping the lower electrode, oxidizing a surface of the oxygen doped lower electrode, depositing a high dielectric constant oxide dielectric material on the oxidized oxygen doped lower electrode, and depositing an upper layer electrode on the high dielectric constant oxide dielectric material.

BACKGROUND OF THE INVENTION

This invention relates generally to capacitors, and more particularly tocapacitors made with high dielectric constant dielectric materialshaving reduced leakage current, and to methods of making such capacitorsand their incorporation into DRAM cells.

The increase in memory cell density in DRAMs presents semiconductor chipdesigners and manufacturers with the challenge of maintaining sufficientstorage capacity while decreasing cell area. One way of increasing cellcapacitance is through cell structure techniques, including threedimensional cell capacitors. The continuing drive to decrease size hasalso led to consideration of materials with higher dielectric constantsfor use in capacitors. Dielectric constant is a value characteristic ofa material and is proportional to the amount of charge that can bestored in a material when the material is interposed between twoelectrodes. Promising dielectric materials include Ba_(x)Sr_((1−X))TiO₃(“BST”), BaTiO₃, SrTiO₃, PbTiO₃, Pb(Zr,Ti)O₃ (“PZT”), (Pb,La)(Zr,Ti)O₃(“PLZT”), (Pb,La)TiO₃ (“PLT”), KNO₃, Nb₂O₅, Ta₂O₅, and LiNbO₃, all ofwhich have high dielectric constants making them particularly desirablefor use in capacitors. However, the use of these materials has beenhampered by their incompatability with current processing techniques andtheir leakage current characteristics. For example, presentRuO_(x)/Ta₂O₅/TiN capacitor structures show several orders of magnitudeleakage degradation after subsequent rapid thermal processing (RTP) at650° C. in a nitrogen atmosphere.

Producing a metal/insulator/metal structure that does not degrade undersubsequent high temperature processing remains an unsolved problem forincorporating high dielectric constant (high K) materials into advancedDRAM cells. A concern with using metal electrodes in the capacitorstructure is that there is vacancy diffusion during subsequent hightemperature treatments. At the electrode interface boundary, it would beadvantageous to have an electrode that could supply oxygen to filloxygen vacancies.

The use of oxygen-doped, sputter deposited platinum (PVD Pt) electrodeshave been proposed in the literature. Y. Tsunemine, et al., “Amanufacturable integration technology of sputter-BST capacitor with anewly proposed thick Pt electrode,” 1998 IEDM 30.3.1. However, PVD Ptelectrodes cannot be used in capacitor container structures. As shown inFIG. 1, when a layer of Pt 12 is sputter deposited in a containerstructure 10, the deposition produces uneven layer thicknesses. Becauseconformal coverage is required for capacitor container structures,sputter deposition cannot be used.

Therefore, there remains a need in this art for improved processes forincorporating high dielectric constant dielectric materials intocapacitor constructions and for capacitors containing these materials.

SUMMARY OF THE INVENTION

The present invention meets these needs by providing a stabilizedcapacitor having improved leakage current characteristics using highdielectric constant oxide dielectric materials, and methods of makingsuch capacitors. By “high dielectric constant oxide dielectric”materials we mean oxides of barium, titanium, strontium, lead,zirconium, lanthanum, and niobium, including, but not limited toBa_(x)Sr_((1−x))TiO₃ (“BST”), BaTiO₃, SrTiO₃, Ta₂O₅, Nb₂O₅, PbTiO₃,Pb(Zr,Ti)O₃ (“PZT”), (Pb,La)(Zr,Ti)O₃ (“PLZT”), (Pb,La)TiO₃ (“PLT”),KNO₃, and LiNbO₃ and having a dielectric constant of at least about 20.

In accordance with one aspect of the present invention, the methodincludes depositing a lower electrode on a semiconductor substrate,oxygen doping the lower electrode, oxidizing an upper surface of theoxygen-doped lower electrode, depositing a high dielectric constantoxide dielectric material on the oxidized oxygen-doped metal electrode,and depositing an upper layer electrode on the high dielectric constantoxide dielectric material. The lower electrode is preferably selectedfrom the group consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys andintermetallic compounds thereof. The upper layer electrode is preferablyselected from the group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os,and alloys and intermetallic compounds thereof. The high dielectricconstant oxide dielectric material is preferably selected from the groupconsisting of Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃.

The oxygen doping is preferably obtained by chemical vapor depositingthe lower electrode in an oxygen-containing environment. By “oxygencontaining environment,” it is meant an atmosphere which containsgaseous oxygen. The upper layer electrode is also preferably chemicalvapor deposited in an oxygen-containing environment. In a preferredform, the method deposits the lower electrode layer and/or the upperlayer electrode using chemical vapor deposition (CVD) techniques.

Another aspect of the invention provides a capacitor including anoxygen-doped lower electrode having an oxidized surface, a highdielectric constant oxide dielectric material adjacent to the oxidizedsurface of the oxygen-doped lower electrode, and an upper layerelectrode adjacent to the high dielectric constant oxide dielectricmaterial. The lower electrode is preferably selected from the groupconsisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and internetalliccompounds thereof. The upper layer electrode is preferably selected fromthe group consisting of TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys andintermetallic compounds thereof. The high dielectric constant oxidedielectric material is preferably selected from the group consisting ofTa₂O₅ and Ba_(x)Sr_((1−x))TiO₃.

Both the lower electrode and the upper layer electrode are preferablydeposited using chemical vapor deposition (CVD) techniques. Also,preferably, both the lower electrode and the upper layer electrode aredoped with oxygen.

The capacitor may also include a first layer of a chemical vapordeposited lower electrode beneath the oxygen-doped layer of the lowerelectrode, and a second layer of a chemical vapor deposited upper layerelectrode adjacent to the first layer of the upper layer electrode.

Accordingly, it is a feature of the present invention to provide astabilized capacitor having improved leakage current characteristicsusing high dielectric constant oxide dielectric materials, theirincorporation into DRAM cells, and methods of making such capacitors.These, and other features and advantages of the present invention, willbecome apparent from the following detailed description, theaccompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of a prior art sputter depositedplatinum electrode in a container structure fragment;

FIG. 2 is a diagrammatic sectional view of a chemical vapor depositedlower electrode in a capacitor container structure fragment inaccordance with one embodiment of the present invention.

FIG. 3 is a diagrammatic sectional view of the chemical vapor depositedlower electrode of FIG. 2 after etching or chemical mechanicalpolishing.

FIG. 4 is a diagrammatic fragmentary sectional view of a containercapacitor structure made according to one embodiment of the presentinvention; and

FIG. 5 is a diagrammatic fragmentary sectional view of an alternativecontainer capacitor structure made according to another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 2, a fragmentary view of a semiconductor substrate anda container capacitor structure is indicated generally by referencenumeral 20. As used herein, the term “semiconductor substrate” refers tosilicon structures including silicon wafers, silicon structures in theprocess of fabrication, a semiconductor layer, including a semiconductorlayer in the process of fabrication, and the like. The semiconductorsubstrate 20 includes a bulk silicon substrate 21. There is a lowerelectrode 22 formed as a layer on substrate 20. Preferably, the lowerelectrode layer 22 has been chemical vapor deposited. Chemical vapordeposition provides conformal coverage, which is necessary for capacitorcontainer structures.

FIG. 3 shows the container capacitor structure fragment 20 of FIG. 2after the lower electrode 22 has been etched back or chemical mechanicalpolished to remove the metal above the upper surface 23 of the containerstructure. Preferably, lower electrode 22 is formed such that it isoxygen doped. A preferred process for oxygen doping is chemical vapordeposition in an oxygen-containing gas environment. Examples of suitablematerials for lower electrode 22 include, but are not limited to, TiN,Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof.

Surface 24 of the oxygen-doped lower electrode 22 is then oxidized. Theoxidation is preferably a gas plasma treatment under oxidizingconditions and is preferably carried out at a temperature of betweenabout 250° to about 500° C., and preferably about 400° C. using a gascontaining either O₂ or O₃. For example, gas plasma may be formed usingmicrowave power on oxygen or ozone gas sufficient to dissociate theoxygen molecules into individual activated atoms. With this step, thesurface of lower electrode 22 is oxidized. This provides at least thesurface, and preferably an upper portion of the electrode, with enoughoxygen so that electrode 22 will be stable with the high dielectricconstant oxide dielectric layer 26.

A layer of a high dielectric constant oxide dielectric material 26 isdeposited on the oxidized surface 24 of the oxygen-doped lower electrode22. Suitable materials for use as the high dielectric constant oxidedielectric include, but are not limited to, Ba_(x)Sr_((1−x))TiO₃(“BST”), BaTiO₃, SrTiO₃, Ta₂O₅, Nb₂O₅, PbTiO₃, Pb(Zr,Ti)O₃ (“PZT”),(Pb,La)(ZrTi)O₃ (“PLZT”), (Pb,La)TiO₃ (“PLT”), KNO₃, and LiNbO₃.Preferably, the high dielectric constant oxide dielectric material isselected from the group consisting of Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃,where x is >0 and <1.

The upper electrode 28 is deposited on the high dielectric constantdielectric layer 26. Upper electrode 28 is preferably chemical vapordeposited in an oxygen environment to provide an oxygen-doped upperelectrode. The upper electrode in the capacitor structure may be madefrom materials including, but not limited to, TiN, W, Pt, Rh, Ru, Re,Ir, Os, and alloys and intermetallic compounds thereof.

Referring now to FIG. 4, the capacitor includes a conductive plug 30 atthe bottom of the container capacitor structure constituting a node towhich electrical connection to capacitor 22 is made. Transistor 32 andfield oxide 34 operate in conjunction with the capacitor.

In an alternative embodiment shown in FIG. 5 (with like numeralsdesignating like structures), the container capacitor structure fragmentincludes a first layer of a lower electrode 21. The oxygen-doped lowerelectrode 22 is adjacent to the first layer of the lower electrode 21.The surface 24 of oxygen-doped lower electrode 22 is oxidized. The highdielectric constant oxide dielectric material 26 is deposited on surface24 of oxygen-doped lower electrode 22. Oxygen-doped upper electrode 28is adjacent to the high dielectric constant dielectric layer 26. Asecond layer of upper electrode 30 is deposited on oxygen-doped upperelectrode 28.

When RuO_(x) is used as the lower electrode 22, where x is >0 and <2,one example of a process for depositing electrode 24 is to depositRuO_(x) using chemical vapor deposition (CVD) of a metalorganicprecursor containing ruthenium. Typically, this process would be carriedout in a reaction chamber at a pressure of about 1 Torr and atemperature of from about 150° to about 200° C. using appropriate gasflow rates for the metalorganic precursor.

RuO_(x) films as deposited include both RuO₂ and Ru phases. The presenceof the Ru phase causes unstable reactions, e.g., the oxidation of Ru toRuO₂ during Ta₂O₅ metal-insulator-metal processing. This is undesirablebecause it deteriorates the oxidation kinetics of Ta₂O₅ and also causesformation of interface defects between RuO_(x) and Ta₂O₅. Oxidization ofthe upper surface of the RuO_(x) film prior to Ta₂O₅ deposition providesa stable RuO_(x)/Ta₂O₅ interface. The overall thickness of the RuO_(x)electrode should be in the range of from about 50 to about 1000 Å, andpreferably between about 100 and 200 Å. The oxidation should be limitedto the upper surface of the RuO_(x) film, penetrating only from about 10to about 50 Å. If the oxidation is carried out through the entirethickness of the electrode, rather than just the surface, the electrodelayer becomes very rough and disturbed.

The oxidation can use low-temperature annealing for a short time. Forexample, oxidation may be carried out at a temperature in the range offrom about 400° to about 475° C. in an atmosphere containing O₂, O₃, orN₂O. The oxidation should be carried out at these relatively lowtemperatures because RuO₄, which is a vapor, forms at highertemperatures, leading to the loss of material from the surface of theelectrode. The oxidation can be performed either before or aftercrystallization of the RuO_(x). Alternatively, rather than depositing alayer of RuO_(x), a layer of Ru metal may be deposited and then thesurface of the electrode oxidized in this manner to form a layer ofRuO_(x).

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes in the methods and apparatusdisclosed herein may be made without departing from the scope of theinvention, which is defined in the appended claims.

What is claimed is:
 1. A method for forming a capacitor comprising:depositing a lower electrode on a semiconductor substrate, oxygen dopingsaid lower electrode, oxidizing an upper surface of said oxygen-dopedlower electrode, depositing a high dielectric constant oxide dielectricmaterial on said oxidize oxygen-doped lower metal electrode, anddepositing an upper layer electrode on said high dielectric constantoxide dielectric material.
 2. A method as claimed in claim 1 wherein theoxygen doping of said lower electrode is achieved by chemical vapordeposition of said lower electrode in an oxygen environment.
 3. A methodas claimed in claim 1 wherein said lower electrode is selected from thegroup consisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys andintermetallic compounds thereof.
 4. A method as claimed in claim 1wherein said upper layer electrode is selected from the group consistingof TiN, W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetalliccompounds thereof.
 5. A method as claimed in claim 1 wherein said upperlayer electrode is chemical vapor deposited in an oxygen environment. 6.A method as claimed in claim 1 wherein said high dielectric constantoxide dielectric material is selected from the group consisting of Ta₂O₅and Ba_(x)Sr_((1−x))TiO₃.
 7. A method as claimed in claim 1 wherein saidcapacitor is in the form of a container structure.
 8. A method forforming a capacitor comprising: chemical vapor depositing a lowerelectrode on a semiconductor substrate in an oxygen environment,oxidizing an upper surface of said lower electrode, depositing a highdielectric constant oxide dielectric material on said oxidized lowerelectrode, and depositing an upper layer electrode on said highdielectric constant oxide dielectric material.
 9. A method as claimed inclaim 8 wherein said lower electrode is selected from the groupconsisting of TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetalliccompounds thereof.
 10. A method as claimed in claim 8 wherein said upperlayer electrode is selected from the group consisting of TiN, W, Pt, Rh,Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof.
 11. Amethod as claimed in claim 8 wherein said upper layer electrode ischemical vapor deposited in an oxygen environment.
 12. A method asclaimed in claim 8 wherein said high dielectric constant oxidedielectric material is selected from the group consisting of Ta₂O₅ andBa_(x)Sr_((1−x))TiO₃.
 13. A method as claimed in claim 8 wherein saidcapacitor is in the form of a container structure.
 14. A method forforming a capacitor comprising: chemical vapor depositing a lowerelectrode selected from TiN, Pt, Rh, Ru, Re, Ir, Os, and alloys andintermetallic compounds thereof in an oxygen environment, oxidizing anupper surface of said lower electrode, depositing a high dielectricconstant oxide dielectric material on said oxidized lower electrode, anddepositing an upper layer electrode on said high dielectric constantoxide dielectric material.
 15. A method as claimed in claim 14 whereinsaid upper layer electrode is selected from the group consisting of TiN,W, Pt, Rh, Ru, Re, Ir, Os, and alloys and intermetallic compoundsthereof.
 16. A method as claimed in claim 14 wherein said upper layerelectrode is chemical vapor deposited in an oxygen environment.
 17. Amethod as claimed in claim 14 wherein said high dielectric constantoxide dielectric material is selected from the group consisting of Ta₂O₅and Ba_(x)Sr_((1−x))TiO₃.
 18. A method as claimed in claim 14 whereinsaid capacitor is in the form of a container structure.
 19. A method forforming a capacitor comprising: chemical vapor depositing a lowerelectrode selected from the group consisting of TiN, Pt, Rh, Ru, Re, Ir,Os, and alloys and intermetallic compounds thereof in an oxygenenvironment; oxidizing an upper surface of said lower electrode,depositing a high dielectric constant oxide dielectric material on saidoxidized lower electrode, and chemical vapor depositing an upper layerelectrode selected from the group consisting of TiN, W, Pt, Rh, Ru, Re,Ir, Os, and alloys and intermetallic compounds thereof in an oxygenenvironment on said high dielectric constant oxide dielectric material.20. A method as claimed in claim 19 wherein said high dielectricconstant oxide dielectric material is selected from the group consistingof Ta₂O₅ and Ba_(x)Sr_((1−x))TiO₃.
 21. A method as claimed in claim 19wherein said capacitor is in the form of a container structure.
 22. Amethod for forming a capacitor comprising: chemical vapor depositing afirst layer of a lower electrode, chemical vapor depositing a secondlayer of a lower electrode, oxygen doping said second layer of saidlower electrode, oxidizing an upper surface of said oxygen-doped secondlayer of said lower electrode, depositing a high dielectric constantoxide dielectric material on said oxidized oxygen-doped second layer ofsaid lower electrode, chemical vapor depositing a first layer of anupper layer electrode on said high dielectric constant oxide dielectricmaterial, oxygen doping said first layer of said upper layer electrode,and chemical vapor depositing a second layer of an upper layer electrodeon said first layer of said upper layer electrode.
 23. A method asclaimed in claim 22 wherein the oxygen doping of said second layer ofsaid lower electrode is achieved by chemical vapor depositing saidsecond layer of said lower metal electrode in an oxygen environment. 24.A method as claimed in claim 22 wherein said first and second layers ofsaid metal electrode are selected from the group consisting of TiN, Pt,Rh, Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof. 25.A method as claimed in claim 22 wherein the oxygen doping of said firstlayer of said upper layer electrode is achieved by chemical vapordepositing said first layer of said upper layer electrode in an oxygenenvironment.
 26. A method as claimed in claim 22 wherein said upperlayer electrode is selected from the group consisting of TiN, W, Pt, Rh,Ru, Re, Ir, Os, and alloys and intermetallic compounds thereof.
 27. Amethod as claimed in claim 22 wherein said high dielectric constantoxide dielectric material is selected from the group consisting of Ta₂O₅and Ba_(x)Sr_((1−x))TiO₃.
 28. A method as claimed in claim 22 whereinsaid capacitor is in the form of a container structure.